On shear in members without stirrups and the application of energy‐based methods in light of 30 years of test observations

Abstract

In a recent paper in Structural Concrete, the authors Dönmez and Bažant explain that the theoretical background of the Model Code 2010 equations for one way and punching shear are not sufficiently grounded in theory and should instead use an energybased size effect law in their formulation to match behavior. To support this claim, finite element simulations were presented. In this paper the basic assumption that an energy-based method must govern the shear failure of beams without stirrups is questioned. These questions are shown to be based on the hardening behavior of aggregate interlock tests and the inability for slip strains to localize during shear failure. In addition to these theoretical arguments finite element analyses were conducted with a constitutive model that is energy-based but that also does an appropriate job at modeling aggregate interlock, an aspect that appears to be lacking in the analyses of Dönmez and Bažant. These new results are shown to better model the test results and confirm that aggregate interlock is important in explaining shear strength and therefore the size effect in shear for slender members. As such any concerns about the safety of the Model Code shear equations appear unwarranted. K E Y W O R D Sdesign codes, energy criteria, finite element simulations, fracture mechanics, model codes, shear

Authors' closure on the discussion of the article: “From experimental evidence to mechanical modeling and design expressions: The Critical Shear Crack Theory for Shear Design” (discussion by Dönmez et al.)

“…It is the belief of the authors that, on the contrary, basing judgment fundamentally on numerical models can be dangerous, since numerical models reproduce the theory they implement but not necessarily the reality. With this respect, it is interesting to note that Dönmez and Bažant 2 ground some of their critics on the basis of a finite element analysis (implementing the M7 microplane model) overestimating actual crack widths by six times 3 which leads to clearly erroneous interpretations and conclusions.…”

Carbon reduction and strength enhancement in functionally graded reinforced concrete beams

“…Firstly, transverse reinforcement is often not present in certain types of bridge components, tunnels, buildings and foundations [6][7][8][9][10][11]. Secondly the shear behaviour of reinforced concrete structures is not well understood and remains at the centre of academic debate [12][13][14][15][16]. Thirdly, these shear failures are mainly governed by the properties of the concrete, rather than those of the reinforcing steel so functional grading holds promise.…”

Assessing beam shear behavior with distributed longitudinal strains

“…The behavior of cracked reinforced concrete (RC) in slender beams has long been a subject of study and debate 1,2 and has been a particularly contentious topic when the issue of shear is considered. 3,4 These debates can range from the behavioral level 5,6 to those focused on how best to design members. [7][8][9][10] Often the best way to make scientific progress with such questions is to turn back to first principles and acquire more and improved experimental data to rule out certain options and focus attention on what might be the most productive ways to provide some future consensus in these debates.…”

“…The behavior of cracked reinforced concrete (RC) in slender beams has long been a subject of study and debate 1,2 and has been a particularly contentious topic when the issue of shear is considered 3,4 . These debates can range from the behavioral level 5,6 to those focused on how best to design members 7–10 .…”